Hi Hose, 

My understanding is that you have several questions here:

1) how can a sales person (or team) be restricted to sell only certain products

2) How do you set up repeating visits without much manual intervention

For 1) If you have a multi-company setting and the salespeople belong to different company units, then product access can be limited by company.  Maybe that is a bit clumsy if you don't really need a multi company setting elsewhere.  

Another option is to get a community or partner module to manage this access based on product categories.  I saw soem modules that allow sales people only to sell products based on matching categories.

You may be able to configure this yourself using product categories or product tags and record rules.

For 2) you can set up a weekly, monthly, or other frequency for repeating services.    Since the Field Services module is based on Projects and tasks you will first need to enable "Recurring Tasks" in the project settings.

Then you will see the green recurring button on the right of the Planned Date fields for each task.  See below.